Certain substituted aryluracils, such as, for example, the compound 3-[4-chloro-2-fluoro-5-(2-oxo-propoxy)-phenyl]-1-methyl-6-trifluoromethyl- (1H,3H)-pyrimidine-2,4-dione, are already known from the (patent) literature (cf. EP 255047). However, these compounds have hitherto not obtained any particular importance.